You say that as if it's a bad thing
Any "camera" company that's not a software company will be relegated to a niche status in not-so-far future. And Nikon is probably leading the pack there.
Software is easy to outsource. Hardware design and manufacturing is the expensive part.
Sony's biggest strength (other than its size) is the fact that it is
an electronics company. A digital camera is, first and foremost, a complex piece of electronics (imaging sensor, support sensors plus attached computers) with a few pieces of glass in front of it. It has much more in common with a digital photocopier or scanner, or any number of pieces of laboratory equipment, than with a film camera. The only real commonalities between film and digital cameras are in the lenses, casing, pentaprisms, etc. - the 'dumb' parts of the machine that just sit there and don't talk much to the rest of the system. Not that these aren't important, but they're the easiest parts to outsource, since they require far less integration into the rest of the electronic, firmware and software setup than, say, a sensor or a CPU.
Sure, Sony has a weakness in optics. But they outsourced this to Zeiss, who, being an optics company, could develop and produce superb lenses, and, not being an electronics or camera company in its own right, had everything to gain and nothing to lose by partnering with Sony to sell more lenses. They also benefited greatly from Metabones, who allowed them to take advantage of everyone else's lens lineups, and helped them along by supplying Metabones adapters with their cameras. And, of course, a takeover of Nikon would add greatly to their capacity to develop and manufacture top-tier lenses in their own right - provided, of course, they can manufacture the bodies to take advantage of them. Which is where they appear to be heading in leaps and bounds at the moment, with respect to mirrorless cameras.